This invention relates to a roof support plate with a pre-formed shape which is flattened to a substantial extent upon emplacement for exerting pressure against the roof of a mine opening where the support plate makes contact. More particularly, the present invention relates to such a roof support plate together with means for maintaining the roof support plate emplaced in such a manner so as to prevent buckling due to reverse bending stresses.
As is known in the art, mine openings have been supported in the past by timbers, concrete, metallic structures and more recently by roof bolts. Because these support devices are of such a well-known character, it is deemed unnecessary to set forth a detailed explanation thereof. Experimental devices have been developed for supporting the entries of mine openings wherein these devices take the form of mobile roof supports that are hydraulically operated. Other suggested measures include the use of plastic adhesive to impregnate the roof strata, or using shotcrete or coating techniques for protecting roof strata from moisture and oxygen. However, these measures are only partially effective in supporting rock strata. In recent years, longwall mining techniques brought about the use of roof chocks and roof shields. These devices are self-advancing hydraulically to hold the roof in the immediate area of the longwall mining machine away from the machine as well as the operators therefor.
As mine openings are developed into deeper strata, the pressure becomes increasingly severe to the extent that experience with such mine operations reveal the development of a far greater number of rib "bumps" and other failures of the rib. The heavy pressures on the rib line tend to spall off the vertical wall whereby the vertical wall appears to behave as a plastic material in failure. Also, as mines are opened into seams characterized by weaker roofs, ribs and bottoms, existing types of roof supports will be even less satisfactory. Known existing types of roof supports fail to solve all the problems presented by present-day mining operations. The more costly types of roof supports, such as reinforced concrete and longwall shields, are quite effective but, at the same time, have the acute disadvantage of excessive cost. The high cost of a roof support in longwall mining operations can usually be tolerated because the roof support elements are not lost but, instead, the elements are advanced as the mining operations proceed on the longwall face. Thus, these elements can be used over and over again. However, in the case of room and pillar mining procedures, expendable roof support techniques are common-place and the short usable life of the panel entries or pillar splits usually do not warrant the cost of expensive roof support devices. A relatively small amount of coal is recoverable from the dispersed openings of the room and pillar mining operations and this severely limits the economical feasibility of roof supports. For these types of mining operations, a serious need exists for an inexpensive but effective roof support.